Boko Haram militants have released 82 of the more than 200 schoolgirls kidnapped in the Nigerian town of Chibok more than three years ago.

It was in exchange for the release of prisoners, according to the presidency, but it is unclear how many.

The girls are understood to have been taken to Banki near the Cameroon border for medical checks.

President Muhammadu Buhari is expected to receive them in the capital Abuja on Sunday.

The mass kidnapping shocked the world, with leading figures and celebrities supporting a campaign to get the girls released.

“For the girls that have returned, their life in captivity has been one that depicts suffering, it depicts the fact that they have been starved, abused,” said Bukky Shonibare, founding member of the ‘Bring Back our Girls’ movement.

“As we have seen before, some of those girls have come back with children. Some of them have also come back with news of how they have been sexually abused.”

As campaigners kept up the pressure, more than 20 girls were freed last October. Others have escaped or been rescued, but 195 were believed to still be in captivity before this latest release.

Boko Haram, which has pledged loyalty to ISIL, wants to carve out an Islamist caliphate.